Light emitting element

Abstract

A light emitting device includes a pair of electrodes facing to each other and a phosphor layer which is sandwiched between the pair of electrodes and includes phosphor particles placed therein. The phosphor particles include an n-type nitride semiconductor part and a p-type nitride semiconductor part, the n-type nitride semiconductor part and the p-type nitride semiconductor part are made of respective single crystals having wurtzite-type crystal structures having c axes parallel with each other, and the phosphor particles include an insulation layer provided to overlie one end surface out of their end surfaces perpendicular to the c axes.

Description

RELATED APPLICATIONS[0001]This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT / JP2009 / 000785, filed on Feb. 24, 2009, which in turn claims the benefit of Japanese Application No. 2008-054725, filed on Mar. 5, 2008, the disclosures of which Applications are incorporated by reference herein.BACKGROUND[0002]1. Technical Field[0003]The present invention relates to a light emitting element / device which is operated by a direct voltage applied thereto.[0004]2. Background Art[0005]Attention has been focused on nitride semiconductors, as practical semiconductor materials for use in light emitting devices, particularly blue-LEDs; blue light emitting diodes and UV-LEDs; Ultra-violet light emitting diodes, among light emitting devices which are operated by application of direct currents thereto. Particularly, attention has been focused on GaN based semiconductors which are represented by gallium nitride (GaN), indium gallium nitride (InGaN) mixed...

AI Technical Summary

Benefits of technology

[0010]However, even when an electroluminescent device is fabricated using phosphor particles according to the conventional technique described in the Patent Document 1, there is the problem of a low light emitting efficiency. There are two reasons therefor. One of them is that such phosphor particles are for exciting the phosphor material through irradiation of an electron beam or irradiation of an ultraviolet ray and, therefore, there is no p-type semiconductor, which reduces the tendency of electrons and holes to recombine to cause light emission. The other one of them is that the conventional technique can not restrict the electric current paths within the phosphor particles, which causes mixture of two electric current paths, which are an electric current path with a lower light emission efficiency and an electric current path with a higher light emission efficiency, thereby resulting in a lower efficiency of the light emitting device. In cases of flowing an electric current through phosphor particles having a wurtzite-type crystal structure for causing light emission therefrom, it is possible to realize a higher efficiency in cases where the electric current path is perpendicular to a direction of the c axis, than that in cases where the electric current path is in the direction of the c axis. This is because in the case where the electric current path is in the direction of the c axis, the energy for use for light emission is partially lost by being influenced by the polarities. Accordingly, in order to cause light emission with a higher efficiency, it is desirable to design the placement of the phosphor particles such that the electric current path is only in a direction perpendicular to the c axis.

[0011]Therefore, it is an object of the present invention to provide a light emitting device having a high light emission efficiency and being capable of having a larger area.

[0018]In the light emitting device according to the present invention, each phosphor particle constituting the phosphor layer includes the n-type nitride semiconductor part and the p-type nitride semiconductor part. This facilitates light emission in each phosphor particle due to combination of electrons and holes, thereby increasing the light-emitting efficiency.

[0019]Further, in the light emitting device according to the present invention, at least one end surface, out of the end surfaces of each phosphor particle which are perpendicular to the c axis, is covered with the insulation film. When the c axe of the phosphor particle is perpendicular to the substrate, the insulation layer of the phosphor particle contacts with an electrode. Thus, the insulation layer prevents an electric current from flowing through the phosphor particle. On the other hand, when the c axe of the phosphor particle is parallel with the substrate, then, the n-type nitride semiconductor part or the p-type nitride semiconductor part at the side surface contacts with the electrodes. Thus, an electric current flows inside the phosphor particle, thereby enabling light emission. As a result, all the electric current paths which contribute to light emission are in a direction perpendicular to the c axe, which realizes high-efficiency light emission, thereby realizing a light emitting device with a high light-emission efficiency.

Problems solved by technology

However, even when an electroluminescent device is fabricated using phosphor particles according to the conventional technique described in the Patent Document 1, there is the problem of a low light emitting efficiency.

The other one of them is that the conventional technique can not restrict the electric current paths within the phosphor particles, which causes mixture of two electric current paths, which are an electric current path with a lower light emission efficiency and an electric current path with a higher light emission efficiency, thereby resulting in a lower efficiency of the light emitting device.

Images